Modern radio receivers are typically equipped with a squelch circuit to disable the receiver's audio amplifier after the radio frequency carrier is no longer being received by the radio. The squelch circuit prevents noise from being heard at the receiver's speaker during normal radio operation. The basic purpose of a noise squelch circuit is to detect the change in the discriminator output noise as the received carrier strength changes. As the RF carrier strength increases, the discriminator noise decreases. Because the higher frequency noise falls or "quiets" more rapidly than low or mid-range noise and provides faster response time, it is used in most noise squelch circuits to determine the squelch decision (whether to squelch or unsquelch the receiver).
Typically, a dedicated squelch circuit includes a: noise amplifier stage; preemphasis filter stage; limiter stage; a high pass filter stage; noise squelch rectifier stage; DC amplifier stage; and finally a comparator stage for comparing the received signal with the preset squelch level in the radio which is normally set by the radio user. More advanced squelch circuits include additional circuits for the prevention of fading and other phenomena associated with temporary changes in the RF signal strength. These dedicated squelch circuits are expensive and demand appreciable area to reside on. Despite their high cost and space requirements, these circuits are indispensable mainly due to their significant performance benefits. As the size of communication devices shrinks with the availability of more powerful processors a trend is seen toward the elimination of dedicated components. Squelch detection has resisted this trend and still demands dedicated circuits. A need is therefore felt for a communication device that enjoys the advantages of squelch without a dedicated squelch circuit.